1. Field of the Invention
The present invention relates to a fuel supply control device for an engine.
2. Description of the Related Art
In a typical engine, the engine, which is provided with a canister for temporarily storing fuel vapor therein, purges the fuel vapor stored in the canister to an intake passage thereof. On the other hand, there is also known an engine in which the fuel injection is stopped when an engine operating condition is determined to be within a selected condition range in which the fuel injection is to be stopped. In this engine, the engine operating condition is determined whether it is within the selected condition range, by comparing at least one engine operating condition parameter, which represents the engine operating condition, such as an engine speed or an opening of the throttle valve, with a corresponding, predetermined reference parameter, such as a reference speed or a reference opening. By temporarily stopping the fuel injection, the fuel consumption can be reduced.
However, if the purging operation is carried out during the stoppage of the fuel injection, the air-fuel mixture formed by the fuel vapor is very lean. Such a lean air-fuel mixture may be exhausted to the exhaust passage without being burned in the combustion chamber.
Therefore, there is known a fuel supply control device for an engine in which the purging operation is stopped when the fuel injection is stopped (see U.S. Pat. No. 4,630,581). This prevents fuel vapor from being exhausted to the exhaust passage without being burned.
In this device, fuel vapor produced in, for example, the fuel tank is introduced into the canister, and is then adsorbed in an activated charcoal arranged in the canister. Therefore, the fuel vapor is prevented from being discharged into the outside air. Next, air is introduced into the activated charcoal, and thereby fuel vapor is desorbed from the activated charcoal and is purged into the intake passage with the air. Namely, a purging operation is carried out. As a result, in the above mentioned device, when the purging operation is stopped, the desorbing of fuel vapor from the activated charcoal is stopped.
However, when a large amount of fuel vapor has already adsorbed in the activated charcoal, or when a large amount of fuel vapor is to be introduced from the fuel tank into the canister, namely, when the storing capacity of the canister is low, if the purging operation is stopped, a problem arises that fuel vapor may be discharged without being stored in the canister. In the above mentioned device, the purging operation is stopped when the fuel injection is stopped, and the fuel injection is stopped regardless the storing capacity of the canister. Namely, the purging operation is stopped regardless the storing capacity of the canister. As a result, the purging operation is stopped regardless the storing capacity of the canister. Accordingly, fuel vapor may be discharged into the outside air, without being stored in the canister.